1. Field of the Invention
The invention relates to a moisture sensor and a steering system.
2. Description of the Related Art
Steering systems have been available which vary the angle of steered wheels by transmitting rotation of a steering shaft resulting from steering of a steering wheel to a rack-and-pinion mechanism as described in, for example, Japanese Patent Application Publication No. 2014-234102 (JP 2014-234102 A). The rack-and-pinion mechanism converts rotary motion of the steering shaft into linear motion of a rack shaft. The rack shaft and the rack-and-pinion mechanism are housed in a housing. Tie rods are coupled to respective opposite ends of the rack shaft via rack ends so as to be able to pivot. The linear motion of the rack shaft is transmitted to the steered wheels via the rack ends and the tie rods.
In the conventional rack-and-pinion steering systems including the steering system in JP 2014-234102 A, rack boots are provided at the respective opposite ends of the rack shaft. The rack boots seal portions between respective ends of the housing and the respective tie rods to restrain external foreign matter from entering a housing space in the housing.
However, when one or both of the rack boots are broken to form an opening in the rack boot through which the housing space in the housing communicates with an external space, foreign matter such as water may enter the housing space in the housing via the opening. Particularly in winter, when water infiltrates into the housing space in the housing and adheres to a belt in a reduction gear apparatus that transmits motive power of a motor to the rack shaft, the belt may be frozen. Consequently, in the steering system described in JP 2014-234102 A, a moisture sensor (moisture detecting apparatus) is provided in a lower portion of the housing in a direction of gravity to detect water infiltrating into the housing space in the housing. The moisture sensor has a pair of electrodes. When a voltage is applied to a first electrode, the moisture sensor detects the water having infiltrated into the housing space if the voltage is applied to a second electrode via the water.
In the steering system in JP 2014-234102 A, the voltage is constantly (or with a constant period) applied to the first electrode in order that the moisture sensor detects water having infiltrated into the housing space. Thus, even during a normal state where no water has infiltrated into the housing space, the moisture sensor keeps consuming power.